Computational modeling in biomechanics has become a standard methodology, both for interpreting the biomechanical and biophysical basis of experimental results and as an investigative approach in its own right when experimental investigation is difficult or impossible. The finite element method is by far the most common numerical discretization and solution technique that has been used. However, the lack of a software environment that is tailored to the needs of the field has hampered research progress, dissemination of research and sharing of models and results. To address these issues, we developed the FEBio software suite during our first funding period (2007-2011), a nonlinear implicit FE framework designed specifically for analysis in biomechanics and biophysics. During the second funding period (2012-2016), we considerably expanded the capabilities of FEBio to model living tissues by implementing chemical reactions between constituents of a mixture. We also broadened the target audience for FEBio by developing a plugin environment that enables investigators to easily add features or interface their own software with FEBio. We also optimized the computational costs associated with these advanced techniques by extending the application of parallel processing. In this competing continuation application, we propose to further expand the capabilities of FEBio by developing and implementing a novel FE framework for simulation of compressible and incompressible computational fluid dynamics, and coupling this framework to existing mixture capabilities in FEBio to enable analysis of fluid-solid interaction problems. We will also enhance algorithmic, analysis and numerical capabilities by implementing efficient iterative linear solvers and preconditioners, new nonlinear solution strategies, adaptive meshing, and mortar methods for mesh tying and contact. We will enhance our preprocessor PreView and post-processor PostView to support the frameworks in the above proposed aims, while continuing to provide exemplary support, training, documentation, and development of the FEBio software suite for the biomechanics research community. Applications of computational biomechanics and biophysics span all fields of the biomedical sciences, including areas as diverse as molecular dynamics, cell motility and mechanics, cardiovascular mechanics, musculoskeletal biomechanics and tissue engineering. The FEBio software suite will facilitate advances in these fields, which in turn will contribute to improved understanding of basic biological and medical questions as well as improved strategies for diagnosis and treatment of disease.